Rebtel, which calls itself the second largest VoIP company after Skype, is launching its SDK, allowing developers to add voice capabilities into their apps. Still in private beta, this set of tools is described as easy to use and will enable interested companies to make their apps and games voice-enabled in as little as 15 minutes and offer their users free VoIP calls alongside cheap calls to landlines and mobile numbers. This in turn opens new revenue potential for developers and right from the start two of them signed up to test it out: Palo Alto-based VIVfone, which offers mobile CRM app that improves the business calling, information gathering and transaction services for consumers; and Stockholm, Sweden-based MobisleApps that develops applications in the lifestyle, dating and productivity categories. These and all other developers integrating Rebtel’s platform also benefit from having all signaling and codec handling wrapped into one easy package, with no back-end support or infrastructure commitment needed.

Sounds pretty compelling but it’s important to add that Rebtel isn’t the first company to offer this capability — Twilio has been offering something similar for quite some time.